Shellfish gauge



FIG. 1 is a top plan view of a shellfish gauge showing my new design, the bottom plan view being a mirror image;

FIG. 2 is a front elevational view;

FIG. 3 is a right side elevational view; and

FIG. 4 is a top, rear, and left side perspective view thereof. 

The ornamental design for a shellfish gauge, as shown and described. 